If you look on their web site most if not all of their trees are mapped and you can easily find their biggest sequoia. They use that tree for introducing staff and interns to tree climbing technique from time-to-time, or at least they used to. The place has changed a lot in the 30+ years I've roamed the property.
This is not their interactive map, simply a flat PDF but the sequoia is located just north of the label "Hemlock Hill Road" on the eastern edge of the "Pines" section label and just west of the "Yews" label on the map. Roughly midway between Bussey Hill to the north and Peters Hill to the south.
-AJ